A strapping head for a strapping machine of the type noted above is exemplified in Pearson U.S. Pat. No. 4,791,968. The strapping head is designed to make a sealless connection in two overlapped layers of steel strap in a tensioned loop, such as the reverse-lock notch or sealless connection exemplified in Tremper et al. U.S. Pat. No. 4,825,512. As exemplified in the Tremper et al. patent, a sealless connection is made from slits, which are punched into the overlapped layers. The slits form interlockable shoulders, which interlock when the loop is released under retained tension.
Generally, as disclosed in the Pearson patent noted above, a set of slitting dies on a pair of pivotally mounted sealing jaws and a longitudinally movable punch on a punch holder cooperate and are adapted to make a sealless connection in two overlapped layers of steel strap in a tensioned loop. A longitudinally movable sealing yoke pivots the sealing jaws by means of cams on the sealing yoke and moves the punch holder via a connection allowing lost motion between the sealing yoke and the punch holder. A pair of pivotally mounted notching cutters on a longitudinally movable notching cutter holder cooperate and are adapted to cut notches in opposite edges of the overlapped layers after the sealless connection has been made. A longitudinally movable notching yoke pivots the notching jaws by means of links and moves the notching cutter holder via a connection allowing lost motion between the notching yoke and the notching cutter holder. The sealing and notching yokes are arranged such that the sealing yoke moves the notching yoke for certain purposes. Strap-cutting elements including a strap cutter are provided, which are adapted to cut the tensioned loop from the remaining strap.
In a sealless connection, in which the overlapped layers include an inner layer and an outer layer, the outer layer is cut from the remaining strap near the slits punched into the outer layer so as to leave a cut end of the outer layer. The outer layer is cut by movable cutter coacting with a stationary cutter. A short portion of the outer layer is left between the cut end and the slits punched into the outer layer and is designated as a strap tail. A common problem is that the strap tail tends to curl outwardly near the cut end due to the stationary cutter acting to separate the outer and inner layers, which thus tends to snag on nearby objects. Such a problem is encountered not only with strapping heads of powered strapping machines of the type noted above, but also with strapping heads of powered strapping machines used to apply metal seals to two overlapped layers of steel strap in a tensioned loop, and also with manual strapping tools.
Prior efforts to deal with the aforenoted problem have focused on flattening the strap tail by causing overtravel of the strap cutter, beyond a point where the outer layer has been cut, before the overlapped layers have been connected. However, those efforts have not been entirely satisfactory, particularly in powered strapping machines of the type noted above. If strap tension is lessened when the outer layer is cut, residual tension may be too small to cause the interlockable shoulders to interlock reliably, which may result in total loss of strap tension and in the outer layer pulling completely out of the sealling mechanism. It may be then necessary to grip the overlapped layers so as to prevent tension loss while the outer layer is being cut or to use separate actuators for sealing and for cutting. If a single actuator is used for sealing and for cutting, optimum final positions of the sealing elements are defined within a narrow window, which does not allow overtravel of the strap cutter for a sufficient distance to flatten the strap tail satisfactorily.
There has been a need, to which this invention is addressed, for an improved mechanism for a strapping head for flattening a strap tail, in a strapping machine of the type noted above.